The present invention relates to glow plugs and more particularly to a high performance glow plug including a heat range indicative colored insulator for use in hobby engines, and particularly in small high performance engines.
One popular form of model car competition is tether racing supported by groups such as the American Miniature Racing Car Association (AMRCA). Tether racing has existed since the 1930's, and the speed and sophistication of the cars and engines has steadily grown. Internal combustion engines used to power model cars, planes, and boats have been refined to an extent that tethered model cars can exceed 200 mph. One important aspect of tuning such internal combustion engines is the selection of a glow plug with the correct heat range. The heat range of the glow plug controls the temperature of the glow plug, and as many as twelve steps in heat range are commonly available. A hotter plug (one with a lower heat range designation) will ignite the fuel in the engine sooner, and a colder plug will ignite the fuel later, thereby affecting the ignition point of the engine. The fuel being used, and other factors such as the exhaust system, also affect the ignition point. All of these engine variables must cooperate to obtain optimal power from the engine. As a result, it is important that the glow plug perform properly, and that the correct heat range glow plug is used.
Various improvements in glow plug construction have been made to ensure proper function is high stress environments. Example of modern glow plugs having such improvements are shown in U.S. Pat. No. 6,346,688 for “Glow Plug with Crimp-secured Washer and Method,” U.S. Pat. No. 6,696,670 for “Glow Plug with Tightly-fit Electrode,” and U.S. patent application Ser. No. 10/781,279 for “Glow Plug,” all having the same applicant as the present application. The '688 patent and the '670 patent are incorporated by reference herein.
Because the small size of glow plugs makes marking difficult, and the stress of preparation for competitive events, there is a likelihood of installing an incorrect heat range glow plug. Because of the extreme environments glow plugs must survive, such as in tethered racing where the lower end of a glow plug can reach in excess of 1000 degrees Fahrenheit, markers such as a colored plastic ring will not survive. A method is thus needed for identifying the heat range of glow plugs, which method can survive harsh environments.